1. Field of the Invention
The present invention relates to a piston coupling mechanism. More specifically, the present invention relates to a piston coupling mechanism provided in a lockup device that functions to lock up a fluid-type torque transmission device by using a piston to press the friction coupling part of a clutch mechanism against the front cover of the fluid-type torque transmission device. The piston coupling mechanism serves to couple the piston and the front cover together in such a manner that they can move in the axial direction but cannot rotate relative to each other. The present invention also relates to a lockup device for a fluid-type torque transmission device. More specifically, the present invention relates to a lockup device provided in a fluid-type torque transmission device equipped with a front cover having a friction surface, an impeller that is fixed to the front cover and forms a fluid chamber, and a turbine arranged opposite the impeller inside the fluid chamber.
2. Background Information
A conventional torque converter has three types of internal bladed wheels (an impeller, a turbine, and a stator). A torque converter represents one type of fluid-type torque transmission device because it transmits torque through fluid enclosed therein. A torque converter is often provided with a lockup device. The lockup device is typically disposed in the space between the turbine and a front cover, which form the fluid chamber of the torque converter. The lockup device is a mechanism that serves to couple mechanically the front cover and the turbine together such that torque can be transmitted directly from the front cover to the turbine.
A conventional lockup device has a circular disc-shaped piston, a drive plate, a driven plate, and torsion spring. The circular disc-shaped piston can be pressed against the front cover. The drive plate is fixed to an outer circumferential part of the piston. The driven plate is fixed to the turbine. The torsion spring serves to couple the drive plate and the driven plate together elastically in the rotational direction. When the lockup device is engaged, torque is transmitted from the front cover to the piston, and from the piston to the turbine through the torsion spring. The torsion spring is compressed in the rotational direction of the torque converter between the drive plate and the driven plate and absorbs and damps torsional vibrations.
There have already been proposals for such a lockup device that has a plurality of friction surfaces to increase the torque transmission capacity. One such device has an elastic coupling mechanism, a clutch mechanism, and a piston. The elastic coupling mechanism is joined together with the turbine. The clutch mechanism has a friction coupling part and rotates integrally with the elastic coupling mechanism. The piston presses the friction coupling part against the front cover.
This kind of device requires torque to be transmitted directly from the front cover to the piston during lockup and several different mechanisms have been proposed for this purpose. For example, in the lockup devices described in Official Gazette No. 11-509611 (Japanese translation of PCT publication) and Laid-Open Japanese Patent Publication No. 10-47453, the piston is mounted to the front cover using a plurality of flat springs. More specifically, a plate member is mounted to the front cover and one end of each flat spring is fixed to the plate member with a rivet(s), a bolt(s), or the like. The other end of each flat spring is fixed to the piston with a rivet(s). Thus, the piston can move axially with respect to the front cover and rotate integrally with the front cover.
In these conventional technologies, a plurality of flat springs is used to couple the piston and front cover together such that they cannot rotate relative to each other and rivets, bolts, or the like are required to fix both ends of the flat springs. Consequently, the number of parts is large, the structure is complex, and the weight is great. Furthermore, the amount of assembly work is large.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved piston coupling mechanism and lockup device for fluid-type torque transmission device equipped with the same. This invention addresses that need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.